C 353 n 
XXVIII. On the parallax of the fxed stars. By John Pond, 
Esq. Astronomer Royal. 
Read June 2 6, 1817. 
In a former Paper on the subject of parallax, I mentioned 
my intention of prosecuting this investigation by means of 
fixed telescopes on a new construction, and which I conceived 
were better adapted to this purpose, than any other instru- 
ment hitherto employed. One of these was directed to 
a, Aquilse, the other to « Cygni. Both instruments have 
answered the intended purpose. The observations of x 
Aquilse were interrupted by some alterations which I found it 
necessary to make in the construction of the instrument ; but 
those of a, Cygni have been continued without intermission 
from the month of January to the present time. 
Strictly speaking, a much longer period would be required 
(even with a perfect instrument) to determine either the ex- 
act quantity of parallax, in case it could be discovered, or the 
limit which it does not exceed, should it prove to be too small 
to be susceptible of observation ; since the uncertainty in the 
annual variation of each star, bears a considerable proportion 
to the quantity to be investigated. 
Notwithstanding, however, this very small uncertainty 
which future observation alone can remove, it appears to me 
that the observations already obtained, afford a proof suffi- 
ciently satisfactory, that the discordances which formed the 
subject of my last communication, must have had some other 
cause than parallax. 
